Mixing alcohol and cannabis: what happens and what are the risks?

Researchers separate two ways of using both substances:

• Simultaneous use means the effects overlap, so you’re feeling both at once. 
• Concurrent use means you use both in the same period but not at the same time – for example, drinking in the evening and using cannabis the next morning, or on different days in the same week.

A study published in Drug and Alcohol Dependence found that on days when participants mixed alcohol and cannabis so that the effects overlapped, they were more likely to report problems.

These included things like:

• Drinking more than planned
• Arguments
• Saying embarrassing things
• Blackouts
• Driving drunk or high
• Nausea
• Hangover

There were fewer of these problems on days when they used both at different times of day.

A controlled study found that drinking a small amount of alcohol before using vaporised cannabis led to higher peak levels of THC in the blood. The researchers say this may help explain the greater impairment seen when people mix alcohol and cannabis.

This was a small laboratory study using vaporised cannabis. It can’t show that alcohol always makes cannabis stronger, or that using cannabis before alcohol is safer. 

But many people who use cannabis with alcohol have bad reactions that they’ve never had with either one alone.

Crossfaded means being intoxicated by weed and alcohol at the same time. It’s slang, not a medical term, and the experience varies a lot from person to person.

• Some people feel relaxed or euphoric
• Others feel dizzy, sick, anxious, badly impaired, or completely overwhelmed.

What one person experiences depends on how much has been taken, the type of cannabis, how it was used, tolerance, and our bodies. 

The impairment from mixing alcohol and cannabis is clear in driving. The Johns Hopkins study tested people’s driving after they took cannabis edibles with a lower amount of alcohol. It found that the combination impaired driving as much as a higher amount of alcohol alone, and sometimes more.

The roadside sobriety tests that police use can miss that impairment. In the study, they only flagged people who had drunk alcohol alone at the higher level, even though driving was clearly worse after cannabis with less alcohol.

It’s common to feel sick, dizzy or anxious, or to vomit, after mixing cannabis and alcohol. These reactions are usually temporary and pass as the substances leave your system. 

They happen because you’ve taken more than your body can comfortably handle. On their own, they’re unpleasant but not usually dangerous.

A green out is an informal term for a particularly bad reaction to cannabis. Symptoms can include:

• Sudden nausea
• Dizziness
• Sweating
• Vomiting
• Anxiety
• Feeling like you might faint

When alcohol is involved too, these symptoms can look a lot like alcohol poisoning. A person who is pale, sweating, vomiting and unable to stand could be greening out, or they could be dangerously intoxicated. If you’re not sure, treat it as an emergency.

Both substances impair driving. You can feel fine to drive and still be impaired, because using them together can make it harder to judge how affected you are. 

Laws on driving after drink or drugs differ from country to country. In the UK and Ireland, it’s illegal to drive while unfit through drink or drugs. 

Police can check for cannabis with roadside drug screening.

• Needing more of either substance to get the same effect
• Repeated bad reactions but continuing to use both
• Using one to manage the effects of the other
• Trying to cut down on either and finding you can’t
• Work or relationships being affected
• Feeling unable to enjoy social situations without both

If you’re noticing several of these, Castle Health can help you understand if you’ve become dependent on alcohol, cannabis or both.

Alcohol can lower your mood in the days after drinking, not just while you’re drunk. Cannabis can increase anxiety, particularly at higher doses or if you’re already prone to it. Both are linked to depression with regular use.

Many people use alcohol or cannabis to cope with anxiety, depression, or other mental health conditions they may or may not have been diagnosed with. That can create a cycle. The mental health condition drives the substance use, and the substance use makes the mental health condition worse.

When both are happening at the same time, clinicians call it a co-occurring condition or dual diagnosis. Addiction and mental health support addresses both together, and tends to be more effective than treating either one alone.

It depends on how much you’ve had of each substance, the type of cannabis (edibles last longer than smoking or vaping), your tolerance, and your body. There’s no single answer. Effects can last anywhere from a couple of hours to much longer if edibles are involved.

No. Using one first doesn’t make mixing them safe. Whichever comes first, the combination makes the effects harder to predict.

Products and doses vary, and so do your personal risks. Check with the clinician or pharmacist who prescribed your cannabis, as they can advise based on your specific treatment.

Yes. Dependence can develop with either substance independently, and using both doesn’t protect you from that. If you’re concerned, an assessment can look at your use of both. You can read more about understanding addiction.

Yes, where clinically appropriate. An assessment considers both patterns together, along with mental health. Castle Health offers both alcohol addiction treatment and cannabis addiction treatment, and the level of care depends on what your assessment shows.